The invention relates to a method of forming a fuel/air mixture in an internal combustion engine with an air intake passage for each cylinder through which air enters the cylinder tangentially under the control of an intake valve disposed in the intake passage and a fuel injector which injects fuel into the cylinder for mixture with the air.
For forming the fuel air mixture in the combustion chamber of each cylinder which is delimited by a piston of the internal combustion engine, an injector injects fuel into the combustion chamber. The combustion air required for forming a combustible mixture is supplied to the combustion chamber by way of at least one intake passage. Admission of the combustion air to the combustion chamber is controlled by an intake valve disposed in the intake passage.
U.S. Pat. No. 2,882,873 discloses an arrangement wherein the combustion air is admitted to the combustion chamber in a flow path which is about tangential to a cylinder wall such that the air spins about the cylinder axis at high speed. Friction of the combustion air at the cylinder wall generates an inwardly directed secondary flow. Adjacent the cylinder wall, the air flow is slowed down by the friction and accordingly is subject to reduced centrifugal forces but subject to the pressure generated by the centrifugal forces experienced by the fast flowing adjacent air layers spinning about the cylinder axis. This generates the secondary air flow along the combustion chamber wall toward the low pressure area in the center of the combustion chamber. Some of the fuel injected into the combustion chamber for mixture with the combustion air is carried by the secondary air flow along the combustion chamber walls to the center of the combustion chamber such that a relatively rich fuel/air mixture is formed in the center of the combustion chamber. The inhomogeneous distribution of the mixture in the combustion chamber results in an increased power output since the compression ratio of the engine can be increased. In addition, a mixture with a localized rich fuel/air mixture reduces fuel consumption and exhaust emissions particularly during partial load operation of the engine. This is especially true for the operation of gasoline internal combustion engines with direct fuel injection since, by forming a relatively rich fuel mixture in the center of the combustion chamber during partial load operation, the electrodes of a spark plug which generally project into the center of the combustion chamber are surrounded by a relatively rich, easily ignitable mixture so that complete combustion of the combustion chamber charge is facilitated.
The intensity of the secondary flow which is required for the return of fuel centrifuged out of the spinning air into the secondary flow along the combustion chamber wall back to the center of the combustion chamber to form the relatively rich mixture depends on the circumferential speed of the air spinning along the cylinder wall. With increasing speed of the air along the cylinder wall, the frictional forces along the cylinder wall increase and the deceleration of the air in the boundary layer along the cylinder wall increases proportionally. The centripetal force which causes the secondary flow and which corresponds to the difference between the centrifugal force of the spinning air flow and the radial pressure gradient accordingly increases proportionally with the circumferential speed of the spinning flow. In the internal combustion engine known from the reference, the spin flow about the cylinder axis is generated by guiding the combustion air in the end section of the air intake passage such that the air enters the combustion chamber in a tangential fashion. The air is guided by a corresponding arrangement and shape of the air intake passage, the shape of the intake valve which includes a guide structure and by guide baffles in the intake passage adjacent the intake valve. Because of the geometrically predetermined guide means for the combustion air flow the speed of spinning flow in the combustion chamber depends exclusively on the air flow volume in the intake passage. However, the combustion air volume required for forming the mixture is predetermined that is it is limited so that, for a wide performance graph range of the internal combustion engine, the reqired intensity of the spin flow and the secondary air flow for forming a fuel/air mixture of optimal quality for the respective engine operating point can not be reached. As a result, the fuel consumption and exhaust gas emissions are relatively high.
It is therefore the object of the present invention to provide a method of forming a fuel/air mixture in an internal combustion engine with direct fuel injection whereby a fuel/air mixture of optimal quality is generated at every operating point of the engine particularly with a view to achieving a combustion with low fuel consumption and low exhaust emission values.